1. Field of the Invention
The present invention relates to methods and apparatus for controlling airflow in a fiber extrusion system and, more particularly, to an airflow control device capable of selectively separating, removing, or re-directing air present in the system to control the flow of the air and fibers in a desired manner.
2. Description of the Related Art
A great deal of development work has ensued since the initial development of the spunbond process in 1959 by DuPont. Much of that work has centered around uniform laydown of the melt spun fibers and properties of the spun web prior to bonding, such as loft or crimp. Additional development work has centered around the nature of the foraminous belt or drum collector, particularly when depositing the melt spun fibers onto solid or microporous substrates.
A schematic of a system 10 for performing a conventional spunbond process is shown in FIG. 1. Spunbond system 10 includes dual fiber extrusion apparatus for deposing fibers on a forming belt at two different locations. Each apparatus includes polymer extruders 12 for respectively melting pellets of two different polymer components (e.g., for forming bi-component fibers) prior to delivery to respective polymer filters 14. Melt pumps and corresponding drives 16 meter the molten polymer streams into spin beams 18, such that the molten polymer is received by spin packs 20 within the spin beams in a controlled manner. The molten polymer streams are distributed in the spin packs and extruded through a spinneret to form extruded fiber filaments 22 of selected cross-sectional geometric configurations.
Below the spinneret, quench air is blown onto the extruded filaments from the sides to at least partially quench the filaments, with some portion of the quench air being exhausted to the sides, as shown in FIG. 1. In each extrusion apparatus, the quenched fibers enter a high speed slot aspirator 24, which draws and attenuates the fibers using compressed air. A portion of the quench air and some of the surrounding ambient room air become entrained with the fibers as they flow from the spinneret into the aspirator. The extruded fibers exit the aspirator along with a substantial volume of entrained air, including air introduced in the aspirator. Upon exiting the aspirator, the drawn fibers are deposited as a web onto a foraminous surface 26 (e.g., a continuous screen belt) and are collected and/or subjected to further conventional or other processing treatments (e.g., bonding, heat treatment, etc.). A suction device 28 positioned below the foraminous surface draws in and exhausts a substantial portion of the air entrained with the filaments arriving at the foraminous surface. Compaction rolls 30 can be used to compact the web to form a loosely bonded fabric. Optional meltblown beam(s) 32 can be used to deposit meltblown filaments in conjunction with or separate from the spunbond filaments. Typical bonding and finishing options include: calendar bonding, through-air bonding, chemical bonding, hydro-entangling, fiber splitting, needle punching, finish application, lamination, coating, and slitting and winding.
The system shown in FIG. 1 is a so-called open system. In some spunbond processes, the filament draw is primarily produced by the quench air which is forced along with the fibers into a draw slot below the quench (a so-called closed system). An example of such a system is disclosed in U.S. Pat. No. 5,814,349, the disclosure of which is incorporated herein by reference in its entirety.
In FIG. 1, the entrained air above the aspirator is due primarily to the quench air, the high speed filaments and the aspirator suction. Below the aspirator, the entrained air is due primarily to the high speed filaments and the high speed air exiting the aspirator as well as the high suction required through the foraminous belt. The problem of handling the large volume of compressed air, quench air and room air induced into the aspirator, and the entrained air from within the room below the aspirator, has been and remains a serious problem despite nearly fifty years of development to try to control the excess air. There is simply too much air causing substantial filament and fabric disturbance, especially in modem high spinning speed processes. In addition, excess suction is required through the foraminous collector to capture all this excess air. Accordingly, it would be desirable to control the airflow in extruded fiber processes, particularly at the point of depositing the fiber filaments on a forming surface or other collection device.